1. Field of the Invention
The present invention relates to a powertrain structure in which power is transmitted from a drive shaft to a driven shaft via a torque damper.
2. Background Art
As a powertrain structure in which power is transmitted between coaxially disposed drive and driven shafts via a torque damper, one is known in which a shaft end of one of a shaft end part of the drive shaft and a shaft end part of the driven shaft is inserted into a shaft hole of the other to join the drive shaft and the driven shaft to each other, and such that the center axes of the drive shaft and the driven shaft may be kept coaxial with each other (refer to e.g. Japanese Patent Laid-Open No. 2014-51120).
Japanese Patent Laid-Open No. 2014-51120 discloses a powertrain structure in which a main shaft in a transmission of a power unit is divided into a first main shaft (drive shaft) and a second main shaft (driven shaft) that are disposed coaxially with each other and a clutch and a torque damper are interposed between the first and second main shafts. A shaft end part of the first main shaft has a decreased diameter and is inserted into a shaft hole with an increased diameter formed in the end part of the second main shaft with the intermediary of a needle bearing, whereby the first main shaft and the second main shaft are coaxially joined to each other to each other in a relative rotatably manner.
The respective fitting parts of the first and second main shafts disclosed in Japanese Patent Laid-Open No. 2014-51120 are pivotally supported by a crankcase with the intermediary of a bearing, and another shaft end part of the first main shaft is pivotally supported by a front cover attached to the crankcase with the intermediary of a bearing. Furthermore, the first main shaft and the second main shaft are pivotally supported by a monolithic support case so that the center axes thereof are kept coaxial with each other structurally.
However, if some sort of external force is applied to the front cover and the front cover gets distorted even somewhat, the coaxial disposition of the center axes of the first main shaft and the second main shaft is deteriorated and a stress other than rotational torque via the torque damper is applied to the fitting parts of the first main shaft and the second shaft, which precludes smooth power transmission, in some cases. In particular, if the drive shaft and the driven shaft are pivotally supported by support cases as separate bodies from each other, it is often difficult to keep the center axes thereof coaxial with each other.